From: Luiz Angelo Daros de Luca <luizluca@...>
Date: 2011-06-24T05:46:43+09:00
Subject: Re: Ruby embed called from a pthread

Hello SASADA,

Thanks for your help but it still does not work.

---
     Luiz Angelo Daros de Luca, Me.
            luizluca@gmail.com



2011/6/23 SASADA Koichi <ko1@atdot.net>:
> Hi,
>
> (2011/06/23 16:37), Luiz Angelo Daros de Luca wrote:
>> Currently, my initialization (ruby_init, RUBY_INIT_STACK,...) run
>> inside the main thread and all following calls works with no problem.
>> However, when the first non-main thread GC, it segfalts. Is it allowed
>> to call ruby from a child thread?
>
> No.
>
> Ruby's GC marks machine stack of (registered) all threads.  However,
> (maybe) your child thread is not registered.
>
> Now, there are no way to register the other thread.
>
>
>> I debugged and what I think that I noticed is that GC scans from
>> current thread stack to the machine "stack end". For the main thread,
>> this is OK. However, when it is a child thread, between the child
>> stack and the main stack, there is some unallocated memory, which
>> segfalts on access. Something like this:
>>
>> [child_stack_start...child_stack_end] unallocated
>> [main_stack_start...main_stack_end]
>>
>> If I disable GC, it runs flawless. Is it a possible solution to
>> disable GC when running a method inside a pthread and reenable it when
>> main thread calls a method? Would it miss (not free) some objects
>> inside pthread stack?
>>
>> One good solution would be some workarround in order to allow calls
>> and GC from any thread as the one I proposed. Is it possible?
>>
>> Another great solution would be to allow all ruby stuck exclusively
>> inside a pthread. This way, I could isolate ruby in a dedicated
>> pthread with a dedicated stack. All other threads would use ruby
>> though this thread. However, my current knowledge tells me that ruby
>> must live inside the main thread (it depends on the main thread stack
>> end address). Am I right? Is something like running ruby from a single
>> pthread possible?
>>
>> The best solution would be to allow ruby initialization inside any
>> pthread and ruby calls from any pthread. I guess ruby is too far away
>> from this one ;-)
>>
>> I was hoping that 1.9.x would help me in any way as it uses pthreads
>> for ruby threads but I noticed no difference.
>>
>> I really searched hard to find a solution before getting to the list
>> but nothing helped. Maybe ruby_bind_stack patch could help but I don't
>> think it would get upstream too soon.
>
> One simple solution is making Ruby thread and communicate with queue or
> something thread-safe data structure.

If I understrood correcly, you suggested that I create a thread inside
ruby world and try to communicate with it from C using a threadsafe
data structure. However, because of the ruby global_vm_lock, the
thread I created in ruby world does not run after my code returns. It
never passes this line:

    native_mutex_lock(&th->vm->global_vm_lock);

It seems that ruby does not use the global lock for C ruby method
(like rb_funcall, rb_eval). I think that it is used only for thread
stuff while inside ruby, unlocking before passing to another thread
and locking when a thread gets control.

So, when my rb_* call returns, global_vm_lock is locked for the main
thread and my ruby thread is not running.

I also get another try forcing my ruby thread to run (using ruby
ConditionalVariable). However, if it sleeps inside ruby, it will get
the same situation of the first case when my rb_* call returns:
"global_vm_lock is locked for the main thread". I tried to sleep my
ruby thread inside C world (using an extension call). In this case, it
is my rb_call that never returns because it cannot get global_vm_lock
back.

I still get no solution.

>
> I think you can run Ruby interpreter in non-main thread.  However, only
> one interpreter.
>

I tried to run all ruby stuff (RUBY_INIT_STACK, ruby_init... ) from a
single thread but it segfaults after some code is loaded, when
requiring some files. Maybe it is the GC that runs and crashes. I
didn't debugged too much this one.

Do you have any project or example that runs ruby inside a thread?

Thanks,

> --
> // SASADA Koichi at atdot dot net
>
>